Coat a 9-inch deep-dish pie plate with cooking spray. Separate crescent rolls into eight triangles and arrange in the pie dish with points toward center. Press to seal seams. In a large skillet over medium-high heat, melt the butter (or heat oil if using oil); add the zucchini, onions and mushrooms, and sauté until tender, about 5 minutes. In a large bowl, beat together eggs, Italian seasoning and mustard; beat to mix. Add vegetables to egg mixture, mixing thoroughly. Pour over crust and bake in preheated 375ºF until a knife inserted near the center comes out clean, about 20-25 minutes.